Drying apparatus



6 8, 1942- J. F. WALSH DRYING APPARATUS Filed March 27, 1940 INVENTOR /aes F Walsh BY ATTORNEYS Patented Dec. 8, 1942 DRYING APPARATUS James F.Walsh, Tuckahoe, N. Y., assignor to Celanese Corporation of America, acorporation of Delaware Application March 27, 1940, Serial No. 326,201 5Claims. (01. aa-im This invention relates to the production of finelydivided, uniformly-sized particles of solids. It relates moreparticularly to the production of uniformly-sized particles of materialsfrom solutions, dispersions and plastic masses containing organicderivative of cellulose and similar materials.

An object of this invention is to produce finely divided particles ofmaterials in a controlled and substantially uniform size.

Another object of this invention is to produce said particles in a rapidand economic manner.

Other objects of this invention will appear hereinafter from thefollowing detailed description.

In many industrial processes it is necessary that solid materials beobtained in a finely divided form. In some instances it is necessarythat the solid particles be produced in ,a dry state from liquidscontaining said materials in solution and in others the solid particlesmay be first produced in a wet state by precipitation from theirsolutions followed by the filtration of the resulting slurries and thedrying of the filtered material. In still other cases, it may be desiredto reduce plastic or other compositions of matter to discrete particles.To accomplish these results various expedients have been employed. Insome instances it has been customary to separate solid materials fromsolutions by spraying them under high pressure through a nozzle andremoving the solvent by evaporation, or by spraying the solution into acoagulating or precipitating bath therefor. The disadvantage of thesemethods lies not only inthat the adjustment of the nozzle is very fineand is easily clogged and therefore requires constant attention, butalso in that the action of corrosive liquids will shorten the life ofsaid nozzles. In addition, there is the ever-present possibility ofleakage or failure of lines in a system under high pressure with injuryto life and property. Where solid plastic masses are to be ground, theuse of mills, etc., has the disadvantage that they are not continuous inoperation and valuable time is consumed, in charging and discharging themills.

I havenow discovered that the preparation of dried, finely dividedmaterials from solutions or plastic masses thereof may be accomplishedby controllably feeding the solutions or fluid masses of the material tobe dried or precipitated to a surface, and positively removing saidsolutions or fluid masses from the surface by picking up the solutionson a second high speed rotating discontinuous surface and throwing orscattering it Instead of feeding said solutions or fluid masses to asurface, they may also be removed in a finely divided form from a bodyof liquid maintained at constant level. When this method is utilized,the discontinuous surface, which is preferably a brush rotating at highspeed, is adjusted so that the moving periphery thereof is in contactwith the liquid to be divided only at the surface thereof. The rotatingsurface may, however, be adjusted so that it dips into the body ofliquid to a greater extent where the viscosity of the liquid makes itdesirable or possible. By suitably adjusting the brush and the level ofthe liquid in relation to the upper edge of the vessel in which it iscontained, the spray may be thrown or scattered over the edge so that itmay fall freely without returning to the body of the liquid. In order todry said materials the spray may be allowed to fall in a heated chamberso that the solvent will be evaporated therefrom or, alternatively, thefinely-divided spray may be allowed to fall into a precipitating orcoagulating bath from which thesolid material may be filtered and thendried in a powder form. Where the material is a plastic mass it may befed to the surfaces in a molten or semi-molten form, and the spraythrown from the second surface may be allowed to fall through cooled airso that the liquid droplets will solidify and produce a finely dividedpowder in a form which is dry, non-agglomerating, and ready forimmediate use.

Various means may be employed for removing the solution or fluid mass asa fine spray from a body of the same or from a surface to which it isfed. Among the most suitable means are brushes rotating at high speed inclose proximity thereto. The bristles of said brushes may be made ofmetal or other strong flexible material which is inert toward thematerials being treated or solvents and which will stand up under thephysical strain, abrasion andflexing to which they are subjected. Othermeans may comprise a discontinuous surfacesuch as a wire screening whichcatchesthe liquid and throws it off in finely divided form,-or springmetal fingers on a roller which pick up the-fluid and then strike astationary' object such as a bar. When released, the

therefrom in the form of a finely divided spray. 65

fingers will spring forward and snap the liquid therefrom in a finespray. The spray may then be treated as described above to obtain thesolid material. A g l The size of the particles obtained may beregulated by varying the diameter of the brush, the speed of rotationand the amount of fluid which is fed to the brush during a giveninterval of time.

Where a small amount of fluid is fed to a brush rotating at very highspeed the resulting particles will be very small. Decreasing the speedof rotation of the brushes or increasing the amount of fluid fed to thebrushes where their speed of rotation is held constant, will yieldmaterials of increased particle size. Where it is undesirable to varythe speed of rotation of the brushes, an increase or decrease of theperipheral speed of the same can be obtained by increasing or decreasingthe diameter 01' the brushes and this in turn will likewise affect theparticle size. Brushes of any practical diameter may be used but Iprefer brushes of from about 6 to about 12 inches in diameter. The speedof rotation may likewise be varied and I preferably use speeds of fromabout 500 to about 1500 revolutions per minute. It is evident that thearrangement of the bristles may also be varied depending on theviscosity and nature of the solution. The brush or other means shouldpreferably be so arranged that the entire surface of the carrying rollmay be swept. By suitable adjustment of the various factors discussedabove, the particle size may be varied at will.

The surface, from which the rotating discontinuous surface, such asbrush, picks up the fluid, may also be a rotating surface such as acylindrical roll, or it may be a flat surface down which the fluid flowsin a layer of appropriate thickness or it may be the top layer of a bodyof the fluid to be divided or precipitated. While either of thesemethods may be used, I prefer to use a rotating cylindrical carryingroll. The fluid may be fed by an adjustable feed pipe to the carryingroll from which it is then removed by the rotating brush. Th thicknessof the fluid layer may be controlled by another roll in close proximityto the carrying roll and the fluid may drop to the space between saidmoving rolls. When the fluid is permitted to flow down a surface, thethickness of the fluid layer may be varied by means of an adjustabledoctor blade or other suitable controlling means.

Where the material which is to be broken down into small particles is aplastic mass such as a plasticized mass of an organic derivative ofcellulose, it may be kept in a fluid plastic condition by using carryingand regulating rolls which are heated and which pick up said plasticcompositions from milling type heated rolls. In some instances it may bedesired to cool said rolls. These expedients may be accomplished byusing hollow rolls through which steam, hot'water or brine may be passedin accord with the result desired.

In order to illustrate my invention, several illustrative embodimentsthereof are shown in the accompanying drawing, in which Fig. 1 is asectional view of an arrangement for finely dividing a solution andpassing it to a precipitating or coagulating bath therefor,

Fig. 2 is a sectional view of an arrangement for finely dividing asolution to produce a dry powder;

Fig. 3 is a sectional view of an arrangement for finely dividing aplastic mass to obtain it in powder form,

Fig. 4 is a detail plan view of an arrangement of the control andvarying rolls and brush, and

Fig. 5 is a. sectional view of an arrangement for removing a. liquid infinely divided form from a body of liquid. It is to be understood thatthe Like reference numerals designate similar parts throughout theseveral views.

In Fig. 1, showing one embodiment of my invention, 5 is an enclosedchamber, and 6 is a feed pipe for delivering a solution of the materialto be obtained in finely divided form to the chamber 5. The solutionfrom the feed pipe 6 drops down into the space formed by a feed controlroll 1 and a carrying roll 8, the feed control roll 1 serving to spreadthe liquid uniformly over the surface of the carrying roll 8. In closeproximity to said carrying roll 8 is a brush 9 revolvin at high speedand adjusted so that it picks up the layer of liquid from the carryingroll 8. The motion of said brush 9 revolving at high speed is such thatit throws the liquid downward in a fine spray where it falls into aprecipi tating bath H! which is slowly agitated by means of a propellerI I mounted on a shaft 42 and journaled in a liquid-tight sleeve l3. Theprecipitating bath'in'which the liquid falls precipitates the solutewhich settles to the bottom of the chamber, and the precipitate may bewithdrawn through the valve M. The precipitating bath may be replenishedthrough valve l5 to keep the bath level constant. The slurry removedthrough valve l4 may be filtered and dried in any suit-' able manner andthe acetic acid or other solvent in the liquid may be recovered in anysuitable manner. While only one brush is shown in Fig. 1, it is alsoobvious that two may be used. The second brush and roll may be suitablydisposed on the opposite side of control roll 1. A second feed pipe maybe provided to form a symmetrical arrangement but this is not necessary.

In Fig. 2 is shown another embodiment of my invention. In this figure l6indicates a chamber into which the solution of the material to beobtained in dry and finely dividedform is delivered through a feed pipeII. The solution is finely divided by means of a feed control roll I8, acarrying roll I 9 and a brush 20 in the manner described above withrelation to the apparatus illustrated by Fig. 1. Dry heated air is blowninto the chamber l6 through an air inlet duct 21, serving to evaporatethe solvent rapidly from the globules or droplets formed by the brush20. The solute falls to the bottom of the chamber in dry powdered formand the solvent laden air leaves the chamber through ducts 22 and 23 andpassed to a solvent recovery system where the solvent may be recovered.Any of the powdered material which is carried by the solvent laden airmay be removed by a cyclone recovery or other suitable system prior tothe delivery of the solvent-air mixture to the solvent recovery system.The main body of the dry, powderedmaterial falls to the bottom outlet 24of the'chamber I6 and may be removed in any suitableuman-'- ner, such asa revolvingworm- 25 or merely-by gravity. If desired the hot air can beintroduced through an opening at a lower part of the chamber instead ofthrough the duct 2|.

In Fig. 3 is shown a modification of :the apparatus suitable forreducing plastic masses to a dry finely divided form. A thermoplasticcomposition 21 is converted or homogenized by the action of heatedmilling type rolls 28 and 29. When the proper degree of plasticity isreached a revolvingwire brush 30 is brought into close proximity to theheated roll 29 and the plastic mass 21 on the roll in the form of a thinlayer is removed therefrom in 'theform of small particles whicharescattered into chamber 26. The finely divided plastic material ischilled and solidified by the action of cold air entering the chamber 26through ducts or pipes 3| and 32. The solidified powdered material fallsto the base 33 of the chamber 26 and may be removed by gravity or by aworm arrangement 25 such as is shown in Fig. 2. The pipe 34 is an outletfor permitting the air in the chamber to escape.

The powdered material is dry, non-agglomerat-- ing and in uniformlyfinely divided form.

In Fig. 5 is shown an arrangement for removing a liquid in finelydivided form from a body of liquid. The body of liquid 35 is containedin a vessel 36. The liquid is fed through a pipe 31, the rate of feedbeing controlled by a valve 38. The vessel may be drained by a valve 38.A brush 40 is mounted in such a manner with relation to the body ofliquid that upon rotation at a suitable speed it will pick up a portionof the liquid and disperse or scatter the same in the form of finelydivided particles or a fine spray. The finely divided particles or.spray thus obtained may be treated in the manner above described withparticular reference to Fig. 1 and Fig. 2. The spray forming means shownin Fig. 5 may be contained within a chamber such as 5 in Fig. 1 or [B inFig. 2 or any other suitable housing depending on the natureof theliquid and the product desired.

My invention is particularly suitable for the precipitation of solutionsof organic derivatives of cellulose and more particularly for theprecipitation of solutions of cellulose acetate after acetylation andageing. Where cellulose acetate is precipitated by pouring the solutioninto a large volume of water or by adding water to the solution, thecellulose acetate is precipitated in a stringy, fibrous form. When thusprecipitated it may be made therein without departing from the spirit ofmy invention.

Having described my invention, what I desire to secure by Letters Patentis:

1. Process for reducing plastic masses to a finely divided form ofsubstantially uniform particle size, which comprises forming a layer ofplastic material on a surface and then brushing said layer while it isin a plastic condition from said surface in the form of particles ofsubstantially uniform size into a chilling medium so as to causesaidparticles to solidify.

2. Process for reducing plastic masses to a finely divided form ofsubstantially uniform particle size, which comprises forming a layer ofthermoplastic material on a heated surface and then brushing said layerwhile it is in a warm, plastic condition from said surface in the formof particles of substantially uniform size into a chilling medium so asto cause said particles to solidify.

3. Process for reducing plastic masses to a finely divided form ofsubstantially uniform particle size, which comprises forming a layer ofthermoplastic material having a basis of cellulose acetate on a heatedsurface and then brushing said layer while it is in a warm, plasticcondition from said surface in the 'form of particles of substantiallyuniform size into a chilling medium so as to cause said particles tosolidify.

4. Process for reducing plastic masses to a finely divided form ofsubstantially uniform particle size, which comprises converting athermoplastic material on a heated surface and then -brushing saidconverted material while it is in a is often difficult to thoroughlywash the cellulose acetate to remove all occluded acids. By my process,however, when the cellulose acetate is precipitated by allowing thefinely-divided spray to fall into a bath of water, the solid particlesof cellulose acetate are obtained in a finely-divided spheroidal formand because of the size, shape by way of illustration and that manyvariations JAMES F. WALSH. I

